Dockboard lip raising mechanism

ABSTRACT

A dockboard lip raising mechanism for the hinged lip of a dockboard including a link attached at one end to the lip and attached at its other end to a crank member, the arrangement being such that the pivotal connection between the link and the crank member moves over-center as the lip nears its raised position, so that the weight of the lip holds the mechanism in the over-center position. When the lip contacts a vehicle platform on lowering with the dockboard, the mechanism is tripped into the under-center position by the slight raising of the lip relative to the dockboard, allowing the lip to fall when the vehicle moves away.

United States Patent Loblick [15] 3,685,076 1, Aug. 22, 1972 DOCKBOARD LIP RAISING MECHANISM [72] Inventor: Dermont F. Loblick, Gibbons, Al-

berta, Canada [22] Filed: June 26, 1970 [21] Appl. No.: 50,098

[52] [1.8. CI. ..14/71 [51] Int. Cl ..B65g 11/00 [58] Field of Search ..14/71 [56] References Cited UNITED STATES PATENTS 3,203,002 8/1965 McGuire 14/71 Primary ExaminerJacob L. Nackenoff Attorney-Cushman, Darby & Cushman [571 Answer A dockboard lip raising mechanism for the hinged lip of a dockboard including a link attached at one end to the lip and attached at its other end to a crank member, the arrangement being such that the pivotal connection between the link and the crank member moves over-center as the lip nears its raised position, so that the weight of the lip holds the mechanism in the over-center position. When the lip contacts a vehicle platform on lowering with the dockboard, the mechanism is tripped into the under-center position by the slight raising of the lip relative to the dockboard, allowing the lip to fall when the vehicle moves away.

6 Claims, 3 Drawing Figures DOCKBOARD LIP RAISING MECHANISM The present invention relates to dockboard installations, i.e., installations which are used to provide a sloping ramp or dock plate connecting the floor of a warehouse bay or like facility to the platform of a vehicle being loaded or unloaded.

Warehouses and like places generally have loading and unloading bays which are raised from ground level so as to be of similar height to the load carrying platforms of the vehicles which are serving the bay. In order for goods to be moved readily from the vehicle platforms and onto the loading bay and vice versa, it is necessary to provide a dockboard which spans the gap between the vehicle and the loading bay, and which also provide a ramp from the loading bay to the vehicle where these are not quite level. Various types of dockboard installations have been developed which include a base part to which the dockboard is hinged at its rear end, and which incorporate a mechanism for raising the dockboard and lowering this onto the platform of a vehicle in the required manner. The dockboards generally include an extendible lip at their outer edge which rests on the vehicle platform, and known dockboards have lips which are hinged to the outer edge of the dockboard and which are raised to form an extension of the dockboard when the dockboard is raised, but which fold away flush with the edge of the loading bay when the board is lowered and not in use.

Many different arrangements are known for raising the dockboard; such arrangements may be mechanical, e.g., using springs, or hydraulic, or partly hydraulic and partly mechanical. An improved hydraulic/mechanical system is described in copending US. Pat. application Ser. No. 50,255.

In addition many different mechanisms have devised for raising the lip of the dockboard in the desired manner. Such lip raising mechanisms are generally required to raise the lip automatically as the dockboard is raised, and to hold the lip in the raised position while the dockboard is lowered onto a vehicle platform, the

' platform itself supporting the dockboard and lip during loading or unloading operations. When the vehicle moves away, it is requiredthat the lip should drop automatically to its vertical position so as not to strike another vehicle backing up to the dockboard. In some known arrangements, a hydraulic cylinder is provided solely for operating the lip; in such cases a fairly complicated control system is required for giving the lip the desired movements. Other arrangements are entirely mechanical, having a system of levers and links connected to the dockboard raising mechanism, the system being arranged to hold the lip extended while the dockboard is being lowered onto a vehicle platform and being adapted to be tripped to release the lip when the lip is raised slightly relative to the dockboard on contacting a vehicle platform.

Known mechanical lip raising mechanisms utilize latching elements, one element of which abuts against a part connected to the lip and which is held in place by friction when the mechanism is supporting the lip weight, but which falls away releasing the lip when the lip is raised slightly on contacting a vehicle platform. An example of such a mechanism is shown in Canadian Pat. No. 767,341. The present invention provides a mechanism which avoids the use of such abutting latching elements, which are subject to wear and to the possibility of going out of alignment.

The present invention utilizes a crank and link arrangement, the connecting pivot of which moves slightly over center, in which position the parts are held by the weight of the lip until the lip is raised slightly on contacting a vehicle platform.

More specifically. a dockboard lip mechanism in accordance with the invention comprises a lip hingedly attached to the forward end of the dockboard, a crank member rotatably mounted on said dockboard, link means pivotally connected at one end to said crank member and having its other end operatively connected to said lip in such manner that lengthwise movement of the link caused by rotation of said crank member in a first direction raises the lip to the extended position. Rotation of the crank member is effected by operating means actuated by movement of the dockboard relative to the base part of the dockboard insulation. These operating means include lost motion to allow for initial raising of the dockboard to an intermediate partly raised position without rotation of the crank member, and are arranged to cause rotation of the crank member in the first direction on raising of the dockboard from the intermediate partly raised position to the fully raised position. In addition, the operating means are unidirectional in that the crank member is enabled to remain stationary while the dockboard is at least partially lowered from the fully raised position. Further in accordance with the invention, the arrangement is such that, as the lip nears its fully raised position, the pivotal connection between the crank member and the link passes over center with respect to the rotational axis of the crank and the link axis, the over-center movement being assisted by the weight of the lip and opposed by gravity or spring forces operating on the mechanism, stop means being provided to limit said over center movement to a small amount.

The weights of the parts of the mechanism, and/or spring forces applied thereto, are such that forces acting on the lip hold the mechanism in the over-center position while the lip is unsupported, and such that the mechanism returns to an under-center position when the crank member is free to move and when the weight of the lip ceases to act on the link.

The stop means limits the over-center movement to an amount small enough that the lip is almost fully ex-- tended when the mechanism is held against the stop means.

Over center movement is accordingly limited to a small amount relative to the movement required for raising the lip from the collapsed position to the extended position.

Preferably, the crank member and the link are connected in such manner that rotation of the crank member in said first direction raises the end of the link attached thereto in nearing the over-center position, the weight of said link being sufficient relative to the other parts of said mechanism to move the crank member and link to the under-center position when the weight of the lip ceases to act on the mechanism. In this case, no springs are required in the construction.

speaking, the link axis lies along the line of action of the i force applied by the link to the crank member, the

over-center condition occuring at the moment when this axis, extended as necessary, passes across the rotational axis of the crank member.

The dead center position may therefore be defined as the position in which the link axis lies in the same plane as the rotational axis of the crank member.

The operating means connecting the crank member to the stationary base member may take a wide variety of forms. However, in the preferred embodiment, the crank member has a moment arm acted upon by a rod extending rearwardly underneath the dockboard, the geometry of the arrangement being such that rearwards movement of the rod rotates the crank member in said first direction and raises the lip to the position in which the lip is extended and the pivot connecting the crank member and the link is in the over-center position. The rod is movable rearwardly by a first arm of a bell crank member, having its second arm attached to a mechanism for raising the dockboard (and thereby being indirectly connected to a stationary base member). The rod is preferably slidable in one direction relative to the bell crank member, this relationship providing unidirectional operation so that the dockboard can be lowered at least partially without interaction between the bell crank member and the rod, so that the crank member remains stationary until the lip has contacted a vehicle platform. In addition, the second arm of the bell crank member is also preferably linked to the dockboard raising mechanism by lost motion means, which allows the dockboard to be raised a certain amount before the lip begins to be raised, so that the lip does not hit a vehicle backed up against the dockboard.

The present invention will be particularly described with reference to the accompanying drawings which show a preferred embodiment of the invention, and in which:

FIG. 1 is a perspective view of a dockboard installation, and

FIG. 2 and 3 are sectional elevations of the same installation in different positions.

As shown in Figs. 1 to 3, the dockboard is shown mounted in a recess or pit in the side of a loading bay 10, so that the top of the dockboard l 1 is level with the loading bay in its horizontal position (Fig. 3). The installation includes a base frame 12 which fits within the pit and which includes longitudinal, transverse and upright members and which forms a support structure for the dockboard and its raising mechanism. The mechanical parts of the installation, i.e., the base frame, the dockboard, and the raising mechanism, form a self-contained unit.

At the rear end of the base frame a special floating hinge is provided including a transverse forwardly projecting rib 15 attached to the upper rear crossmember 16 of the frame, which rib is engaged by a horizontal flange 17 projecting rearwardly from the rear end of the dockboard. The flange 17, which is in this case the top flange ofa channel member, rests on the top of the rib, and abuts against a shallow step 18 at the rear edge of the rib formed by an upwards projection of the crossmember 16. The rib 15 has a downwardly sloping and slightly curved upper surface, which allows the dockboard to move between its extreme positions while maintaining an almost gap-free transition between the upper rear surface of the base structure and the dockboard. This hinge is also floating in that it allows a slight rocking movement of the dockboard to occur about its fore-and-aft axis, whereby the forward end of the dockboard can rest flush with a vehicle platform even if the platform is not level. Clearly, a rearwards force must be maintained on the dockboard to prevent dislocation of the hinge.

The hydraulic/mechanical system for raising the dockboard, which is the subject of copending U.S. Pat. application Ser. No. 50,255, comprises basically a lever 20 and a link 21, connected together at their inner ends by a pivot 22, the outer end of the lever 20 being connected to the dockboard l l by means of a pivot 24, and the outer end of the link 21 being connected to the base by a pivot 25. Pivot 25 is situated so as to be at all times forward of the pivot 24. A hydraulic cylinder 26 is pivotally attached to the base by means of the same pivot 25 which holds the outer end of the link, and the piston rod 27 of this cylinder is connected to a pivot point 29 on the lever intermediate the end pivots 22 and 24. In operation, as the piston rod 27 extends, the lever 20 is caused to rotate primarily about pivot 22, where it is held by the link 21, so that the outer end-of the lever magnifies the movement of the piston rod in raising the dockboard. In order for the piston rod to exert adequate turning moment on the lever in the fully collapsed condition (Fig. 3), the intermediate pivot point 29 is spaced above a line joining the end pivot points 22 and 24, so that the lever takes the form of an obtuse-angled bell crank.

As will be seen from Fig. 1, the lever 20 consists of two parallel plates, linked by rods forming the pivots 22, 24 and 29. The outer end of the piston rod 27 acts at the center of pivot rod 29. The center of pivot rod 24 is attached to a sleeve member 31 extending fore-andaft of the dockboard and rotatable on a pin held by a bracket 32, and this arrangement allows rocking motion of the dockboard about a fore-and-aft axis (as permitted by the floating hinge) to occur without bending the raising mechanism. The link 21 is also formed by two parallel link members, spaced on opposite sides of the cylinder 26, and connected to longitudinal base members 34 by pivot rod 25 which also provides the pivotal mounting for the base of cylinder 26.

The present invention is concerned with a novel lip operating mechanism by means of which a lip 40 hinged to the outer edge of the dockboard is raised while the dockboard is raised, and remains in a raised condition until tripped by contact with a vehicle platform, or until the dockboard is finally lowered.

The lip operating mechanism comprises essentially a moment arm 44 depending from underneath the lip, to which are pivoted at 43 two parallel links 42 passing rearwardly through an opening in the front flange 46 of the dockboard. The rear ends of links 42 are pivotally connected at 48 to one arm of a crank member 49 which is rotatably mounted at 50 on a bracket 51 fixed to the lower side of the dockboard. The arrangement is such that on rotation of the crank member in the anticlockwise direction (as seen in Figs. 2 & 3), the links 42 are moved forwardly so raising the lip to its extended position. After the lip has reached its fully raised position, the pivot 48 passes over-center with respect to the rotational axis 50 of the crank member and the link axis; i.e., the link passes beyond a position in which the link axis lies'in the same plane as the rotational axis of the crank member 49, this position representing a dead center position for the pivot 48 and corresponding to the fully raised position of the lip. Movement beyond the dead-center position is assisted by the weight of the lip, which urges the links rearwardly but this over-center movement is limited to a small amount relative to the movement required for raising the lip from the collapsed position to the extending position by a stop 56 engaging the crank member. The ends of links 42 attached to the crank member 49 are raised during this over-center movement, so that gravity forces oppose this over-center, movement. Accordingly, if the weight of the lip on the mechanism is relieved, as by the lip contacting a vehicle platform when the dockboard lowers, while the crank member is free to rotate, the weight of the links returns the mechanism to the under-center position.

The crank member 49 is connected to a stationary part of the base frame through the intermediary of the dockboard raising mechanism, and through operating means arranged to cause anticlockwise rotation (as seen in Fig. 2) of the crank member as the dockboard is raised said operating means having lost motion allowing the crank member a limited amount of free rotation after the dockboard has been lowered from its uppermost position. These operating means include a yoke member 54 pivotally connected at 53 to a rear arm of crank member 49, the yoke member being attached to a rod 55 extending rearwardly underneath the dockboard. The crank member 49 is in the form of a bell crank having an obtuse angle defined by its two arms, i.e., the central pivot 50 is displaced below a line joining the end pivots 48 and 53. The arrangement is such that on pulling of the rod 55 rearwardly the member 49 is rotated anticlockwise so raising the lip and causing the mechanism including the links 42 to pass over center, so that by virtue of the rearwards force applied to links 42 by the lip weight once the lip has been raised by pulling the rod 55 the lip remains raised without any further tension being maintained in rod.

The inner end of rod 55 carries a slidable crossmember 57, the travel of which is limited by a nut 58 secured to the screwed outer end of the rod. The crossmember 57 carries a pivot pin at each end which engage in opposite arms of a bracket 60, this bracket forming a first arm of a bell crank member 61 pivoted at 62 to a longitudinal member 63 fixed to the under side of the dockboard. The second arm of bell crank 61 is provided with a slot in which a pin 64 is slidable, this pin 64 connecting two side plates of a link 65, one of which side plates is extended and pivoted at 66 to the intermediate pivot rod of the lever 20. The link member 65 thus forms the connecting link between the dockboard raising mechanism and the lip raising mechanism.

The operation of the lip raising mechanism is as follows:

In the initial horizontal position of the dockboard (shown in full lines in Fig. 3) the pin 64 of link 65 is at the outer end of the slot in bell crank 61, the crank 61 is in a position in which the slotted end is close to the dockboard, the rod 55 is thus in a forward position, and the lip 46 is hanging vertically. As the dockboard is raised by extension of piston rod 27 and the mechanism described previously, the intermediate pivot point 29 (which coincides with pivot 66) of the lever 20 moves away from the underneath of the dockboard. pulling with it the link 65 and causing pin 64 to move to the inner end of its slot. Since the pin 64 is free to move in this slot, and since the link 65 is free to swivel about pivot point 66, no turning movement is experienced by crank 61 in this initial raising movement, which continues until the dockboard has been raised to an intermediate partly raised position about halfway up to its final position. Due to the lost motion provided for in the linkage by the slot in the second arm of bell crank 61, crank 49 is not rotated and the lip 46 remains hanging during this initial movement, and does not catch against a vehicle backed up against the dockboard.

When the pin 64 reaches the inner end of the slot in bell crank 61, further raising of the dockboard causes the link 65 to come into tension, and this rotates the crank 61 anticlockwise (referring to the sideelevational views). This rotation moves the rod 55 rearwardly, and causes the crank member 49 to swivel and raise the lip 40 to its extended position, in the manner already explained, the pivot 48 moving to the overcenter position.

From this upper position with the lip raised, the dockboard is slowly lowered until the lip 40 comes to rest on the platform of a vehicle. The engagement of the lip on the platform then supports the dockboard while a vehicle is being loaded or unloaded.

These movements may be made automatic by connecting cylinder 26 to a hydraulic circuit by means of which the cylinder is extended by operation of a hydraulic pump, the cylinder being automatically lowered slowly when pump operation ceases.

During this initial lowering movement, bell crank 61 rotates slightly clockwise, but member 57 slides on the rod 55 so that although tension in the rod is removed, the rod is not forced forwardly and the lip remains raised by virtue of the over-center position of the pivot 48. The sliding of member 57 on the rod 55 provides a unidirectional interconnection between the bell crank member 61 and the crank member 49, so that the rod is not forced forwardly to cause premature collapse of the lip. In other words, the operating means is unidirectional in that the crank member 49 is enabled to remain stationary while the dockboard is at least partially lowered from the fully raised position. When the lip engages the vehicle platform, it is raised slightly relative to the dockboard so that links 42 are put in tension and, since rod 55 is not under tension, the crank 49 rotates slightly clockwise until, due to the weight of links 42, the pivot point 48 eventually assumes a below center position with respect to pivot points 43 and 50.

Thus the mechanism which holds the lip raised is tripped once the lip has come into contact with a vehicle, and when the vehicle drives away the lip automatically falls, with rod 55 sliding within member 57.

As is clear from Figure 3, the dock plate not only provides an upwards ramp for vehicles having a platform which is higher than the loading bay, but also provides a downwards ramp for use when the vehicle is slightly lower than the loading bay. In order for the docking plate to reach the lowest position, which is shown ghosted in Figure 3, the hydraulic controls are operated so that the dockboard rises in the manner previously described until the lip 40 has been fully extended, and then falls slowly under gravity with fluid being returned from the cylinder 26 into a fluid reservoir, until the lip finally contacts the vehicle, for example when the lip is near to the lowest position shown in Figure 3. The engagement of the lip on the vehicle platform trips the lip raising mechanism as described, and when the vehicle has moved away the lip drops and the dockboard continues to descent until a timed limit switch 70 is actuated by the end of the lever 20. This limit switch causes an electrical contact to be made to start the hydraulic pump motor to pressurize cylinder 26 causing the dockboard to rise just above the horizontal position, after which the limit switch 70 deenergizes the pump motor and the hydraulic circuit again allows the dockboard to descend under gravity. The outer edge of the lip 40 is caught in a support bracket 71 forming the outer edge of the frame 12, and all parts of the mechanism are at rest in the position shown in full lines in Figure 3. In this position, the engagement of the lip 40 in the bracket 71 gives firm support to the dockboard.

The limit switch 70 also comes into action in the event of the dockboard being raised and lowered without contacting a vehicle platform. In this case, the dockboard again lowers itself to the lowest position of Fig. 3 at which the lever actuates the timed switch 70 and the dockboard is again raised to a positionin which the lip can fall down and be caught behind the outer edge of bracket 71. In this case, the lip operating mechanism is automatically collapsed by an adjustable stop 73 positioned on the frame to strike the rear por tion of crank 49 when the dockboard is in its lowest position, so rotating the crank 49 and tripping the lip.

Clearly, various modifications are possible within the scope of the invention. For example, instead of relying on the weight of links 42 to return the mechanism from the over-center to the under-center positions, spring means could be used to perform this function; in this case the crank member could easily be designed to rotate in the opposite direction, moving the links downwardly as the lip is raised. Accordingly, it will be understood that the term over center means a slight movement beyond the position in which the pivot 48 is aligned with axis 50 of the crank member and with the link axis irrespective of whether the final position is above or below this aligned position. Also, it is within the scope of the invention to arrange for the link to be so connected to the lip that rearwards movement of the link raises the lip; in this case the over'center position occurs after the pivotal connection between the crank member and the link has been drawn back to its rearmost position so that the link axis passes across the crank member axis.

The operating means for rotating the crank member may take a very wide variety of forms; for example, this means might simply be a flexible element connecting an arm of the crank member to the base framework, the flexible element being slack enough to allow the dockboard to be partially raised before movement of the crank member occurs.

lClaim:

l. A dockboard lip raising mechanism comprising a dockboard hingedly mounted on a stationary base part. a lip hingedly attached to the forward end of the dockboard soas to form an extension thereof when raised, a crank member rotatably mounted on said dockboard, a link pivotally connected at one end to said crank member and having its other end operatively connected to said lip, said link being operative to transmit motion from the crank member to the lip and to raise the lip from a collapsed position to its extended position on rotation of the crank member in a first direction, the link being arranged so that the link axis lies in the same plane as the rotational axis of the crank member when the lip is in its fully raised position, said position of the lip representing a dead center position for the pivotal connection between the link and the crank member, and wherein rotation of the crank member in said first direction causes said pivotal connection to move beyond said dead center position to an over-center position, stop means being provided to limit said over-center movement to a small amount relative to the movement required for raising the lip from the collapsed position to the extended position, the mechanism being such that the forces acting downwardly on the lip are sufficient to maintain the over-center position of the mechanism while the lip is unsupported and wherein operating means are provided connected to said crank member and actuated by movement of the dockboard relative to said base part, said operating means including a bell crank pivoted to said dockboard, one leg of said bell crank being operatively connected to said crank member, the other unsupported, of said bell crank being connected by linkage means to said base part for lost motion transmittal of forces from said base part to said bell crank and being arranged to cause rotation of said crank member in said first direction on raising of the dockboard from an intermediate partly raised position to a fully raised position at which position said operating means causes the said pivotal connection between the crank member and the link to move to the over-center position.

2. A mechanism according to claim 1, wherein the crank member and the link are connected in such manner that rotation of the crank member in said first direction raises the end of the link attached thereto in nearing the over-center position, the weight of said link being sufficient relative to the other parts of said mechanism to move the crank member and link to the under-center position when the lip is raised slightly relative to the dockboard as by contacting a vehicle platform.

3. A mechanism according to claim 1 wherein the link is connected to the lip by means of a moment arm extending downwardly from the lip and pivotally connected to the outer end of the link, the arrangement being such that rotation of said crank member in said first direction moves the link forwardly to raise the lip.

said rod and another arm connected by a link to a dockboard lifting lever, said lever being connected at one end to the dockboard and having its other end connected via a link to the base part.

6. A mechanism according to claim 4, wherein said rod has a part fixed thereto which engages the bell crank member when the lip is in a collapsed position. 

1. A dockboard lip raising mechanism comprising a dockboard hingedly mounted on a stationary base part, a lip hingedly attached to the forward end of the dockboard so as to form an extension thereof when raised, a crank member rotatably mounted on said dockboard, a link pivotally connected at one end to said crank member and having its other end operatively connected to said lip, said link being operative to transmit motion from the crank member to the lip and to raise the lip from a collapsed position to its extended position on rotation of the crank member in a first direction, the link being arranged so that the link axis lies in the same plane as the rotational axis of the crank member when the lip is in its fully raised position, said position of the lip representing a dead center position for the pivotal connection between the link and the crank member, and wherein rotation of the crank member in said first direction causes said pivotal connection to move beyond said dead center position to an over-center position, stop means being provided to limit said over-center movement to a small amount relative to the movement required for raising the lip from the collapsed position to the extended position, the mechanism being such that the forces acting downwardly on the lip are sufficient to maintain the over-center position of the mechanism while the lip is unsupported, and wherein operating means are provided connected to said crank member and actuated by movement of the dockboard relative to said base part, said operating means including a bell crank pivoted to said dockboard, one leg of said bell crank being operatively connected to said crank member, the other leg of said bell crank being connected by linkage means to said base part for lost motion transmittal of forces from said base part to said bell crank and being arranged to cause rotation of said crank member in said first direction on raising of the dockboard from an intermediate partly raised position to a fully raised position at which position said operating means causes the said pivotal connection between the crank member and the link to move to the over-center position.
 2. A mechanism according to claim 1, wherein the crank member and the link are connected in such manner that rotation of the crank member in said first direction raises the end of the link attached thereto in nearing the over-center position, the weight of said link being sufficient relative to the other parts of said mechanism to move the crank member and link to the under-center position when the lip is raised slightly relative to the dockboard as by contacting a vehicle platform.
 3. A mechanism according to claim 1 wherein the link is connected to the lip by means of a moment arm extending downwardly from the lip and pivotally connected to the outer end of the link, the arrangement being such that rotation of said crank member in said first direction moves the link forwardly to raise the lip.
 4. A mechanism according to claim 1 wherein said operating means includes a rod pivotally connected to an arm of the crank member, said rod being movable by said bell crank and having slidable connection therewith.
 5. A mechanism according to claIm 1 wherein said operating means includes a rod pivotally connected to an arm of the crank member, said rod being movable by said bell crank having one arm co-operating with said rod and another arm connected by a link to a dockboard lifting lever, said lever being connected at one end to the dockboard and having its other end connected via a link to the base part.
 6. A mechanism according to claim 4, wherein said rod has a part fixed thereto which engages the bell crank member when the lip is in a collapsed position. 